The defective elements from indium bump preparation in FPA fabrication are tested by optical microscopy and FPA testing bench. Results show that the defective elements from indium bump fabrication include connecting defective elements and missing defective elements. It is easy to identify missing defective elements by FPA testing bench because the response voltage of defective elements is zero and response voltage of other elements around defective element is higher than that of normal elements. And it is difficult to identify connecting defective elements by FPA testing bench because the response voltage of connecting defective elements is basically the same as that of normal elements. The defective elements from indium bump fabrication are due to the indium bump with connecting or missing caused by the process of photolithography, eroding and lift-off. Fabrication process such as photolithography, eroding and lift-off is optimized to reduce defective elements from indium bump fabrication.
Optimization of indium bump preparation in infrared focal plane array (IRFPA) fabrication is presented.
Reasons of bringing defective pixels during conventional lift-off and cleanout process in fabrication of indium bump are
discussed. IRFPAs are characterized by IRFPA test-bench. Results show that defective pixels of InSb IRFPA are owing
to indium bumps connecting through indium residue on the surface of wafer. The characteristic and configuration of
defective pixels of InSb IRFPA are given and analyzed. A method of reducing defective pixels through optimizing liftoff
and cleanout process in InSb IRFPA is proposed. Results prove that this method is effective.
For counteracting background current of photoconductive (PC) PbS detector, an example of layout design and analyze 1×128 linear PbS infrared focal plane array (IRFPA) detector using resistance selection of blind sensitive element is given. 1×128 linear PC PbS infrared focal plane array detector is fabricated and characterized by IRFPA test-bench. Results show that average responsivity of detector is 4.19×106V/W; average detectivity of detector is 5.79×109cm•Hz1/2•W-1.
Material characteristics of InSb wafer and Si wafer are fundamental factors to fabricating qualified infrared focal plane array (IRFPA). Parallelism and flatness of wafer are critical to yield and reliability of large format IRFPA. Influence of materials’ parallelism and flatness on indium bump growing, flip-chip bonding and back thinning in the fabrication of large format IRFPA is analyzed. Parallelism of material brings additional nonuniformity to IRFPA. Parallelism after back thinning is only determined by the parallelism of readout integrated circuit (ROIC) and isn’t affected by that of detector. Influence of material flatness is non-contacting or bad-contacting during flip-chip bonding, which results in bad pixels of IRFPA. According to actual fabrication condition of IRFPA, flatness of one single detector and ROIC chip should be better than 1 µm. Parallelism of ROIC chip should be better than 2 μm. Optical flat is the most convenient approach for InSb material morphology test. Utilizing higher indium bump and press in flip-chip bonding, designing larger contact metal under indium bumps or fabricating indium bumps with smaller diameter in center, selecting distribution of chips on wafer are put forward to reduce influence of morphology. Yield of large format IRFPA is improved.